I thank Julius Blumfeld for his various kind words and especially for his welcome criticisms. I shall do my best to reply to these.1

It is true that justificationists, both libertarians and non-libertarians, often vehemently reject the critical-rationalist approach. And this means that the book faces an extra but, I believe, necessary hurdle. (There is also the problem of the relative lack of interest in libertarian ideas in the UK, which is possibly why there are more reviews of this book on amazon.com.) I do hold that libertarian thinkers cannot “prove or justify libertarianism.” However, I should add that would-be justificationists often do something valuable nevertheless, namely explaining libertarianism. For so-called justifications (foundations, support, etc.) are often really explanations of how libertarianism is supposed to work. But these explanations are themselves, perforce, ultimately conjectural and rarely as clear as they might be if their proponents understood this. So, although they cannot achieve their ostensible purpose, I am far from dismissing everything written in the name of 'justification'
as being a complete waste of time. Conversely, I note that critical rationalists sometimes fail to explain how they think something works, apparently out of the fear of that conjectural explanation being seen as an attempted justification. But it is sometimes merely bemusing to hear a bold and tersely expressed conjecture without any explanation of what it involves and its context.

Blumfeld suggests that I have left “certain questions tantalisingly unanswered.” I suggest that a closer reading of the book would reveal some answers to these questions after all. But no doubt they could have been more clearly stated, which I shall attempt here.

He asks first, “Why are liberty, welfare and anarchy compatible?” The answer is that it is partly causal. It is partly a contingent fact about the free market as an aspect of liberty, for instance, that it increases welfare. We can easily imagine systematic market disasters that would do no such thing. People are individually aiming for utility (welfare) and the market and voluntary interactions are usually the route they take. So the apparent direction of causality may depend on what you are looking at or the way you are looking at it. It is also partly “tautological” or, rather, a priori . For we see that anarchy is an extreme form of liberty where no one is ruled. And we see that liberty, as not being proactively imposed on, is ipso facto desirable (and thus far welfare enhancing). But I argue, at some length, that any conceptual connections are not merely tendentious or sleights of hand. They withstand critical scrutiny as plausible accounts of what these things must be about. There are certainly conceptual connections between my “definitions of liberty and welfare” (also anarchy and rationality) but not enough, I think, to say that they are really “similar” definitions. For I allow the clear possibility that they could diverge, but I bring in evidence and arguments that they do not do so as a matter of reality. So I don't think that “at some deeper level they are the same thing or ... both manifestations of some deeper underlying principle.”

Blumfeld suggests that Escape from Leviathan “provides only limited guidance as to how we are to derive rules and laws that will maximise liberty.” However, it explains how self-ownership and private property are derived from maximising liberty. So there is a presumption that these will often be sufficient to do the job, and that ought to be “concrete” enough. Where there are difficult and novel cases then we sometimes have to resort to the original formula. For instance, David Friedman cites various cases where absolute property rights do not work. One case is of any trivial light generated on your property not being allowed to cross onto my property without my permission. My solution is that my 'suffering'
the light is a lesser imposition (usually too trivial for compensation) than your having to go without a light or possibly have perfectly light-proof curtains at all times. We must prefer the lesser imposition as maximising liberty (and, as Friedman does realise, utility). Having such an abstract formula seems to be the opposite of pragmatism. So, to respond to Blumfeld's interest, I think that only the liberty formula can ultimately “derive libertarian laws and rules.” Economic analysis can assist in this but economics itself is silent on what is libertarian unless it uses some extra-economics conception of liberty. Economics is best at showing where utility lies.

I fully admit that my theory of, libertarian, liberty “does not always fit comfortably with the meaning that most libertarians would attach to it.” It is quite different from many other definitions or theories (for instance, by rejecting coercion and the harm principle as at all relevant and rejecting self-ownership and private property as central, rather than derived). Many of those other libertarian definitions of liberty are vague or tacit. I am trying to capture the theory of liberty that is presupposed or logically entailed, whether or not this is realised. I originally wrote of liberty as being the absence of initiated imposed costs (on persons by other persons) and then immediately shortened this for ease to “the absence of imposed costs.” I now think it is slightly clearer to write of the “absence of proactively imposed costs.” But that is the definition in a pre-propertarian world. Once property has been derived as being libertarian (when acquired and held in a way compatible with liberty), then it is clearer in everyday life to speak of liberty as the 'absence of proactive impositions (or possibly
restrictions)' where property is assumed to be libertarian. Thus the proactively imposed damage to Blumfeld's bumper must be “a loss of liberty” in the defended sense. Admittedly, this is an unusual way to describe it. But perhaps it sounds less odd to say, which is equivalent, that he has been 'proactively
restricted' in his enjoyment of his property. Libertarianism does entail having all the enforceable rules and laws ultimately in terms of liberty. This can occasionally sound odd, but that is what libertarianism is about. Without it we have undecideable or incomplete rules and laws from a libertarian viewpoint, and possibly additional inconsistent principles.

Now for the “scope of the conjecture”, in particular the thought experiment posed. I state in the book that it is supposed to be a practical conjecture about the real world. Liberty and welfare have a systematic tendency to go hand in hand. We can see that they will occasionally conflict (in particular at the micro and personal level: someone might steal to save his life) but this will not be systematic enough for us to alter the rules to increase liberty or welfare. Is Blumfeld's “small but identifiable group of people [who] would be indisputably worse off in a world of maximum liberty” a refutation? First, note that this is a mere, and non-concrete, logical possibility. I ruled out those as refutations of the practical thesis that the compatibility thesis is supposed to be. It is hard to say much more without more, imagined, details. For instance, the group of people who have their hearts set on ruling other people, perhaps even having them as slaves, might themselves be less happy all their lives. But to give into them would surely decrease overall liberty and overall welfare in reality. How can liberty and welfare plausibly clash in reality? We can relevantly discuss any putative cases, but it is not enough merely to suppose that they logically might. However, I can answer Blumfeld's final question clearly: no, 'welfare'
does not “mean welfare for literally everybody.” The thesis is not that everyone will always have more welfare if liberty is maximised. The extreme classical liberal (or libertarian) compatibility thesis is that there is no systematic practical clash between maximising liberty and maximising welfare such that we have to choose between maximising the one or the other. For instance, if the state really improved welfare (via state legislation, education, healthcare, etc.) compared to the market and charity, then we would have just such a clear practical clash. But as we both know, it does not.